Multiple myeloma (MM) is a plasma cell malignancy historically defined by the presence of end-organ damage, specifically, hypercalcemia, renal failure, anemia, and bone lesions (CRAB features) that can be attributed to the neoplastic process. In 2014, the International Myeloma Working Group (IMWG) updated the diagnostic criteria for MM to add specific biomarkers that can be used to make the diagnosis of the disease in patients who did not have CRAB features. In addition, the update allows modern imaging methods including computed tomography (CT) and positron emission tomography-CT to diagnose MM bone disease. These changes enable early diagnosis, and allow the initiation of effective therapy to prevent the development of end-organ damage in patients who are at the highest risk. This article reviews these and several other clarifications and revisions that were made to the diagnostic criteria for MM and related disorders. The updated disease definition for MM also automatically resulted in a revision to the diagnostic criteria for the asymptomatic phase of the disease termed smoldering MM (SMM). Thus the current diagnosis and risk-stratification of SMM is also reviewed in this article. Using specific prognostic factors, it is possible to identify a subset of patients with SMM who have a risk of progression to MM of 25% per year (high-risk SMM). An approach to the management of patients with low-and high-risk SMM is discussed.
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